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"There are now five different lines of observational evidence pointing to the existence of Planet Nine," said Konstantin Batygin, a planetary astrophysicist at Caltech in Pasadena, California, whose team may be closing in on the heavenly body.

"If you were to remove this explanation and imagine Planet Nine does not exist, then you generate more problems than you solve.

"All of a sudden, you have five different puzzles, and you must come up with five different theories to explain them."

Batygin and his co-author on a new study, Caltech astronomer Mike Brown, described the first three clues last year, and two more have since emerged.

One suggested Planet Nine could have tilted the planets of our solar system during the last 4.5 billion years, explaining a longstanding mystery.

The other involved objects from the Kuiper Belt that orbit in the opposite direction to everything else in the solar system.

"No other model can explain the weirdness of these high-inclination orbits," Batygin said.

"It turns out that Planet Nine provides a natural avenue for their generation."

The remaining step, of course, is to find Planet Nine itself.

If discovered, it would be a homecoming of sorts, or at least a family reunion.

Over the past 20 years, surveys of planets around other stars in our galaxy have found the most common types to be "super Earths" and their somewhat larger cousins - bigger than Earth but smaller than Neptune.

While it may sound enough to make women experiencing the nausea of early pregnancy scoff, researchers have suggested morning sickness can take a toll on expectant dads, too.

New research out of Australia's Edith Cowan University examined the experience of 300 expectant couples and found more support was needed for the partners of women experiencing nausea and vomiting during pregnancy.

The study aimed to gauge expectant fathers' awareness of what their partners were going through, and the affect it had on the dads themselves.

The study found 82 per cent of fathers were aware that their partner experienced morning sickness.

Of these, 20 per cent reported no nausea or vomiting, mild 30 per cent, moderate 37 per cent and severe 13 per cent.

The partners of all 11 women formally diagnosed with hyperemesis gravidarum, reported the nausea and vomiting was severe.

Researchers asked expectant fathers about their partners' condition and their own mental health and found a significant increase in dads' anxiety levels.

Although there was some support available for pregnant women during pregnancy, the fathers were often left to fend for themselves, lead researcher Julie Sartori said.

"The study showed that in families where the mother experienced moderate or severe morning sickness, fathers reported much higher levels of anxiety."

That anxiety was linked to five main factors - disruption to work, feelings of frustration and helplessness, concern over depression in their partner, worry for the developing baby, and a "sense of being manipulated".

"There needs to be an active approach from medical practitioners and antenatal care providers, towards expectant fathers in cases where morning sickness is moderate or severe," Sartori said.

"Professionals would normally focus on the wellbeing of pregnant women, however engaging the father as well may help relieve reported anxiety and improve outcomes in the long term."

Can night shift make you fat?

A new study has drawn a link between night shift work and obesity. Photo / 123RF

Researchers from the Chinese University of Hong Kong analysed data from 28 previous studies to find that night shift work was connected to a 29 per cent increase in a worker's chance of becoming overweight or obese.

The weight was mostly centred around the worker's stomachs, say the scientists, and mostly affected those who worked nights permanently, rather than those who worked rotating shifts.